Dewaxing process



Oct 29, 1.963 A. M,su vA ETAL DEWAXING PROCESS 2 Sheets-Sheet 1 FiledDec. 29. 1959 Oct 29, 1963 A. M. SILVA ETAL DEWAXINGPROCESS 2Sheets-Sheet 2 Filed Dec. 29, 1959 United States Patent O This inventionrelates -to the removal Lof wax or waxlike materials from mixturescontaining the same. In `accordance with one embodiment this inventionis directed to the dewaxing of waxy materials by a combination ofoperations involving solvent dewaxing and urea dewaxing or urea complexformation. In the practice of this invention the following materials ormixtures thereof can be dewaxed or fractionated by the removal of wax orwaxlike materials the reform: waxy petroleum fractions such as waxylubricating oils, fatty acids, fatty oils, vegetable oils, animal oilsand fats and fish oils and the like.

In the solvent dewaxing of waxy petroleum streams and the like it is thepractice to admix the waxy petroleum to be dewaxed with a liquiddewaxing solvent and -to cool the -resulting admixture to a suitable-low dewaxing temperature to precipitate a substantial portion of thewaxy material. The resul-ting precipitated wax is then removed byltration from the resulting dewaxed petroleum.

In :a urea `dewaxing or urea complex formation fractionation operationurea is added to a material containing components which are capable of`forming solid complexes with urea. These complexes, such las ureacomplexes with the straight chain ihydrocarbons, n-paraffins in themolecular weight range C6-C25 and higher, form at relatively lowtemperatures, such as a temperature in the range 50-150" F., more orless. The urea complex formation operation is usually carried out in thepresence of an accelerator such as methanol, isopropyl alcohol, ormixtures thereof and the like, i.e. materials which tend to act both asa solvent for the urea and the mixture undergoing fractionation by ureacomplex formation thereby bringing about conditions wherein a moreintimate contact takes place between the urea and the urea complexVforming components of the mixture. Following the formation of the solidurea complexes these complexes are usually removed by ltration and thensuitably treated in the presence of a solvent and at la relatively hightemperature at which the complexes de'- compose, usually above about 150F., to break the complex and to separate the urea from the complexforming components.

It is an object of this invention to provide an improved ureafractionation or complex formation operation.

It is another object of this invention to provide `an improved dewaxingoperation involving in combination solvent dewaxing and urea complexformation.

Another object of this invention is to provide a process for dewaxingwaxy petroleum streams.

Still another object of this invention is -to provide a combina-tiondewaxing operation whereby low pour point substantially completelydewaxed lubricating oils are obtained.

Yet another object of this invention is to provide an improved processfor the fractionation of fatty `acids and 3,1859452 Patented Oct. 29,l963 rice oils and vegetable oils and animal oils and the like for therecovery of special wax-like materials therefrom.

How these yand other lobjects of this invention are attained will becomeapparent in the light of the accompanying disclosure made with referenceto the accompanying drawings, wherein:

FIG. I is a schematic flow diagram of a dewaxing operation in accordancewith the practice of this invention and applicable to the dewaxing ofpetroleum streams, and wherein:

FIG. II is a schematic flow diagram of another dewaxing process inaccordance with this invention.

In accordance with at least one embodiment lof the practice of thisinvention at least one of the foregoing objects will be achieved.

It has now been discovered that `an improved fractionation or waxseparation process involving urea complex formation is obtained bycarrying out the urea complex formation operation in the presence of adewaxing solvent and in the presence of a minor amount yof waterdissolved in said dewaxing solvent. More particularly, in accordancewith `this invention `an improved fractionation or dewaxing operationinvolving urea complex formation is effected by subjecting a mixturecontaining wax lor waxlike components, at least a portion of which formsolid complexes with urea, to solvent dewaxing to precipitate said waxor said wax-like components. Following the precipitation of these wax orwax-like components the remaining mixture, now dissolved in the dewaxingsolvent, is subjected to contact with urea in the presence of a minoramount of water, which is either extraneously added dur-ing or justprior to the urea contacting operation or which is 'already incorporatedon the dewaxing solvent, even during the aforesaid solvent dewaxingoperation. A minor amount of water incorporated in the dewaxing solvent,such as an amount of water in the range G25-2.5% by vol. based ron thedewaxing solvent or solvent plus the aforesaid remaining mixture, anddissolved therein, is usually suicient.

It is seen therefore that in ,accordance with one embodiment thisinvention involves a fractionation process employing two special`dewaxing or fractionation steps: (l) a solvent dewaxing operationwherein the mixture undergoing fractionation is cont-acted with adewaxing solvent under conditions to effect the precipitation of solidwax or wax-like materials therefrom `and (2) after separation of thesesolid wax or wax-like componen-ts, such as by ltration, the remainingmother liquor lor filtrate is contacted with urea under complex formingcondi-tions to form solid urea complexes with lthe wax or wax-likecomponents in the mother liquor which are capable of forming solidcomplexes with urea.

In accordance with a particular embodiment of this invention theresulting formed solid urea complexes are separated, such as byfiltration, and the remain-ing filtrate fractionated by distillation toseparate dewaxed material and dewaxing solvent therefrom. The dewaxingsolvent, especially the aromatic hydrocarbon portion or wax solventportion thereof, is then employed to break or decompose the previouslyseparated urea complexes to yield solid urea and wax or wax-likecomponents dissolved in the aromatic hydrocarbon portion of the dewaxingsolven-t.

In a solvent dewaxing operation the dewaxing solvent employed,particularly in the practice of this invention, is an admixture of anormally liquid aliphatic ketone, an anti-solvent or non-solvent forwax, such as an aliphatic ketone containing from 3 to 12 carbon atomsper molecule and a normally liquid aromatic hydrocarbon, a wax solvent,such as an aromatic hydrocarbon containing from 6 to 12 carbon atoms permolecule. Suitable aliphatic ketones which make up a dewaxing solventfor use in accordance with this invention include acetone, methyl ethylketone, ethyl ethyl ketone, methyl isobutyl ketone, ethyl isobutylketone, methyl isopropyl ketone, methyl n-butyl ketone, propyl n-butylketone, propyl isobutyl ketone, and the various lower and highermolecular weight homologs, and mixtures thereof.

Suitable normally liquid aromatic hydrocarbons which make up a dewaxingsolvent employed in the practice of this invention include benzene,toluene, the xylenes, ortho-xylene, meta-xylene `and para-xylene,ethylbenzene lalong with the various other monoor poly-alkyl orhydrocarbyl substituted benzenes containing up to 12 carbon atoms permolecule.

In the practice of this invention it is preferred to employ as thedewaxing solvent a mixture of methyl ethyl ketone and toluene, such as a50/50 mixture or a mixture containing 20-80% by vol. aliphatic ketonesuch as methyl ethyl ketone, or other suitable aliphatic ketone ormixtures thereof, and Sil-20% by vol. aromatic hydrocarbon such astoluene or other suitable normally liquid aromatic hydrocarbon. Y

In the actual solvent dewaxing operation the mixture containing wax orwax-like materials, such as a waxy petroleum fraction or a mixture offatty oils or fatty acids, is contacted with a suitable dewaxingsolvent, usually in an amount 0.5-10.0, more frequently in the range 16, parts by vol. dewaxing solvent per part by vol. mixture undergoingdewaxing.

The dewaxing operation is carried out at a relatively low temperature,such as a temperature in the range 30 F. down to about 40 F., more orless, the actual dewaxing temperature employed depending upon theparticular mixture to be dewaxed, the make up or composition of thedewaxing solvent employed, the amount of wax or wax-like components inthe mixture undergoing dewaxing and the amount of wax or wax-likecomponents desired to be precipitated during the dewaxing operation.

Following the dewaxing operation the resulting precipitated wax orwax-like components are separated, usually by iiltration, to yield aslack wax or relatively crude wax product fraction and a mother liquoror iiltrate. Following this wax separation operation the wax is thenusually recovered as product by suitable treatment which might involvewax repulping or an additional dewaxing (deoiling) operation.

It is well known that urea is capable of forming solid complexes withmolecules having a substantially straight chain conguration, such as thenormal paraliins, the normal oleiins, fatty acids, etc. It is also wellknown that thio-urea is capable of forming solid complexes withmolecules which have a relatively slightly branched molecularconfiguration, such as the isoparaflins, the isoolens, etc.

Urea readily forms solid complexes with straight chain hydrocarbons,particularly the straight chain parainic hydrocarbons having a molecularweight in the range C6-C25, at relatively low temperatures, such as aternperature in the range 40-150 F., usually in the range 60-l25 F. Ithas been observed that among those components which are capable offorming solid complexes with urea the higher molecular weight componentis capable of forming complexes with urea at a temperature higher thanthe relatively low molecular weight component. Although emphasis hasbeen made herein of the fact that urea forms solid complexes withstraight chain hydrocarbons, as indicated hereinbefore, it is also knownthat urea is capable of forming solid complexes with non-hydrocarbonmaterials but which possess a substantially straight chain molecularconfiguration, such as the straight chain fatty acids, fatty alcohols,in the molecular weight range C55-C25 and higher and accordingly thepractice of this invention, as indicated hereinabove, is also applicableto the fractionation of mixtures containing these materials.

In a urea fractionation operation formation of solid urea complexes isexpedited by the presence of a solvent which is a mutual solvent forurea and for the mixture or components thereof which are capable offorming solid urea complexes. Accordingly in a urea fractionationoperation it is usual to employ materials such as methanol, isopropanol,isobutanol and ethanol, and the like in order to expedite urea complexformation.

Following the separation of the solid urea complexes, in the usual typeof fractionation process involving urea complex formation the solid ureacomplexes are decomposed into their respective components, urea and thewax or wax-like materials complexing therewith by heat, such as byexposing the urea complexes to a temperature at which the complexes arenot stable, such as a temperature above about 150 F., e.g. a temperaturein the range 15G-250 F. Alternatively the urea complexes maybedecomposed or broken by contact with a solvent for urea such as water.Usually a combination of heat and a solvent, either a urea solvent or asolvent for the other wax or wax-like component of the complex, isemployed.

Referring now in detail to the drawings, and in particular to FIG. Ithereof which schematically illustrates one embodiment of the practiceof this invention, as applied to the dewaxing of a waxy petroleumfraction, a waxy petroleum oil in the lubricating oil boiling range,such as a petroleum fraction having a boiling range in the range SOO-900F., more or less, is supplied from a source, not indicated, via line 11into solvent dewaxing unit 12 wherein it is contacted and admixed with adewaxing solvent, such as a 50-50 mixture of methyl ethyl ketone andtoluene in the proportions 3 parts by vol. de-

Waxing solvent to l part by vol. waxy oil. The admixture is chilled to asuitable low temperature, such as a temperature in the range 40 to minus40 F. to precipitate the waxy hydrocarbons therefrom, the dewaxingsolvent being supplied from a source, not shown, to solvent dewaxingunit 12 via line 14. The resulting admixture of solid wax, dewaxingsolvent with the partially dewaxed oil dissolved therein is suppliedfrom solvent dewaxing unit 12 via line 15 to iilter 16. Desirably filter16, as schematically illustrated, is a rotary dewaxing lter. Withinfilter 16 the solid wax is separated and removed via line 18 as slackwax for eventual treatment and recovery of a product wax. The iltrate,dewaxing solvent containing the partially dewaxed oil dissolved therein,is removed from iilter 16 via line 19 and introduced into urea dewaxingunit 20.

Within urea dewaxing unit 2i) the filtrate is admixed with urea suppliedthereto from a suitable source, not shown, via line 2li. The ureaintroduced into urea de# waxing unit 2o is supplied in the form of solidurea, or in the form of a supersaturated solution or slurry, such asadmixed with additional dewaxing solvent, or component thereof or chargeoil which has already been solvent dewaxed and urea fractionated inaccordance with this invention. Also Water from a suitable source, notshown, is introduced into urea dewaxing unit 20 via line 22. The amountof water from the extraneous source thus introduced into urea dewaxingunit 20 is added in a relatively minor amount as compared with thefiltrate or dewaxing solvent therein, and is in the range G25-2.5% byvol. based on the tiltrate or dewaxing solvent.

Upon 4admixture of the urea with the filtrate in the presence of waterwithin urea dewaxing unit 20' urea conn plex formation between the ureaand the waxy straight chain hydrocarbons contained in the partiallydewaxed oil within the iiltrate takes place substantially immedi.

ately, the urea complex formation being substantially complete in lessthan about 30 minutes, such as in about 2-20 minutes.

Following the for-mation of the solid urea complexes the resultingadmixture of urea-wax complexes, plus dewaxed oil Iand dewaxing solvent,together with any excess urea (the urea is desirably employed in anamount in substantial excess over that required to form complexes withall the waxy straight chain hydrocarbons in the oil introduced into ureadewaxing unit 20) is supplied from urea dewaxing uni-t 20 via line 24 tofilter 25. Desirably filter 2S is of substantially the same constructionas filter 16 and may be a vacuum rotary filter or a pressure rotaryfilter. Within ,filter 25 the solid urea-wax complexes are separatedyand recovered therefrom via line 26 and -the remaining filtrate ormother liquor is recovered from filter 25 via line 28.

The urea-wax complexes recovered from filter 215 via line 26 areintroduced into urea-wax complex breaker 29 wherein, desirably, it issubjected to an elevated complex-breaking temperature, such as atemperature of at least about 150 F., such as a temperature in the rangeG-200 F., e.g. 170 F., in the presence of a Wax solvent which is also anon-solvent for urea. The wax solvent is added to complex breaker 29'from ya source, not shown, -via line 3i?. -In accordance with aparticu-lar embodiment of the practice of this invention the wax solventemployed within complex breaker 29 is the same as the wax solvent oraromatic hydrocarbon employed as a component of the dewaxing solventemployed within the solvent `dewaxing unit 12. Accordingly the waxsolvent supplied via line 3G to complex breaker 29 is toluene.

Within complex breaker 29 ldue to the application of heat in thepresence of the added wax solvent, toluene, the urea-wax complex isdecomposed into solid urea and wax which is dissolved in the waxsolvent. The resulting solution of wax in the wax solvent, toluene, isrecovered from complex breaker 29 via line 31 for the eventual treatmentand recovery of a product wax. The solid urea resulting from thebreaking of lthe urea-wax complexes is removed from complex breaker 29via line 32 and recycled via line 21 to urea dewaxing unit 20 to contactadditional partiaily dewaxed oil for the removal of additional waxyhydrocarbons therefrom.

The filtrate comprising dewaxed oil `and dewaxing solvent is recoveredfrom filter 2S via line 2S and supplied to methyl ethyl ketone stripper34 wherein methyl ethyl ketone is recovered overhead via line 35 andadvantageously recycled to solvent dewaxing unit 12 via line 14 tocontact additional waxy oil feed.

The bottoms issuing from methyl ethyl ketone stripper 34 via line 36 andcomprising dewaxed oil and toluene is supplied to toluene stripper 38wherein toluene is recovered overhead via line 39 for recycle via line14- to solvent dewaxing `unit 12 to contact additional waxy oil feed.Desirably a portion of the toluene recovered overhead from toluenestripper 38 via line 39 is supplied via line 40 and line Sii to complexbreaker 29 to contact the urea-wax complexes therein to effect theirdecomposition.

As indicated hereinabove water from an extraneous source, not shown, isadded to urea dewaxing unit via line 22 and is incorporated in the ureadewaxing reaction admixture therein. In the preferred practice of thisinvention this water added to urea dewaxing unit 20 is recovered duringthe dewaxing solvent recovery steps, especially in the methyl ethylketone recovered overhead via line 35 from lmethyl ethyl ketone stripper34 and recycled via line 14 to the solvent dewaxing unit 12. lnaccordance with this preferred embodiment it is seen that theoil-containing fil-trate supplied via line 19 to the urea dewaxing unit20 will already contain the desirable requisite amount of waterdissolved therein.

Product, dewaxed oil is recovered as a bottoms product via line 41 fromtoluene stripper 38.

Referring now in detail to FIG. II of the drawings which schematicallyillustrates vanother embodiment of the practice of this invention andwherein the same reference numbers employed in FIG. I have also beenemployed to designate the same or comparable equipment, the embodimentschematically illustrated in FIG. II differing from that illustrated inFIG. I in the treatment of the urea complex reaction admixturecontaining excess urea, solid urea-wax complexes, dewaxed oil anddewaxing solvent issuing kfrom the urea dewaxing unit, the primarydifference residing in the fractionation of the urea complex reactionmixture to separate therefrom the ketone component of the dewaxingsolvent prior to the separation therefrom of the solid urea-wax complex.As indicated in IFIG. II waxy oil is supplied via line 11 to solventdewaxing unit 12 wherein it is contacted with dewaxing solvent suppliedvia line 14. The resulting admixture of solid wax, partially dewaxed oiland dewaxing solvent is supplied `from solvent dewaxing unit 12 via line15 to filter 16. The separated wax is recovered there-from as slack wax,via line 13 for the eventual recovery of product wax.

The filtrate comprising partially dewaxed oil and dewaxing solventrecovered from filter 16 via line 19 is suppiied to urea dewaxing unit20 wherein it is contacted with an excess of solid urea introducedthereinto via line 21. Additionally water is supplied, as may berequired, via line 22 to urea dewaxing unit '20 so that the -dewaxingsolvent therein is saturated with respect to water or contains an amountof water dissolved therein in the range (12S-2.5 by vol. based on thefiltrate or the dewaxing solvent.

There is recovered from urea dewaxing unit 20 a resulting react-ionadmixtur comprising excess solid ureaq solid urea-wax complexes, dewaxedoil and dewaxing solvent. The reaction adrnixture is supplied from ureadewaxing unit 2.0 via line 24 to methyl ethyl ketone stripper 34 whichlis operated under conditions, preferably under vacuum, so as to avoidexposing the ureawax complexes therein to a temperature high enough todecompose these complexes. Desirably methyl ethyl ketone stripper 34 isoperated under conditions by cmploying a reduced pressure therein suchthat the ureawax complexes therein are not exposed to a temperature inexcess of F., but at a temperature sufficient to distill overhead methylethyl ketone which is desirably recycled via line 35 and line 14 tosolvent dewaxing unit 12 to contact additional waxy oil feed.

There is recovered as bottoms from methyl ethyl ketone stripper 34 theremaining reaction admixture comprising excess urea, solid urea-waxcomplexes, dewaxed oil and the remaining component of the dewaxingsolvent, toluene. This bottoms fraction is recovered from methyl ethylketone stripper 34 via line 36 and transferred to pump 37 whichtransfers the aforesaid bottoms admixture via line 43 to filter 25.

Within filter 2.5 the excess of so'lid urea and the solid urea complexesare separated and recovered therefrom via line 26 and transferred tourea-wax complex breaker 29'. Within complex breaker 29 the urea-waxcomplexes are contacted with wax solvent, preferably the wax solventcomponent, toluene, of the dewaxing solvent supplied via line 30 undercomplex-breaking conditions, such as a temperature of at least about 150F. to effect decomposition of the urea-wax complexes into theirrespective components, solid urea and wax. The wax is dissolved in thewax solvent employed within complex breaker 29 and is recoveredtherefrom via line y31 for eventual treatment and recovery as a productwax fraction. The urea thus regenerated from the urea-wax complexeswithin complex breaker 29 is separately recovered and transferred vialine 32; and line 21 to urea dewaxing unit 2.0J to contact additionalpartially dewaxed oil supplied thereto from dewaxing filter 16 and line19.

The filtrate recovered from filter 25 and comprising substantiallycompletely dewaxed oil together with resid- ,ual dewaxing solvent,now-substantially only toluene, is

supplied via line 28 to toluene stripper 38. Toluene is recoveredoverhead therefrom via line 39 and is recycled lvia line 14 to solventde-waxing unit 12 to contact additional waxy oil feed. Further,desirably a portion of the toluene stripper 33 via lline 39 istransferred via line 40 and line 39 to complex breaker 29 to serve asthe wax solvent therein to decompose the urea-wax complexes. Product,dewaxed oil is recovered from toluene stripper 38 via line 41.

As in the case of the combination dewaxing operations schematicallyillustrated in FIG. I the dewaxing solvent, particularly the methylethyl ketone recovered overhead via line 35 from methyl ethyl ketonestripper 34, ccntains substantially all of the water originally suppliedto urea dewaxing unit via line Z2. that suicient water is maintained andrecycled within the system so that the addition of extraneous water tourea dewaxing unit 20 via line 22 need not always be required save tothe extent necessary to maintain the desired water concentration, G-2.5%by vol. in the filtrate or dewaxing solvent and as may be required tomake up actual physical losses, physical or in the recovered products.

The following is exemplary of the practice of this invention and of theadvantages derivable therefrom. A light paratnic lubricating oil wassolvent dewaxed by employing a 50/50 mixture of methyl ethyl ketone andtoluene at a solvent to oil dosage of 3:1, the solvent dewaxingoperation being carried out at a temperature in the range 0 to 30 F.Following the solvent dewaxing operation the filtrate therefrom, afterseparation of the precipitated Wax, containing dewaxed oil and dewaxingsolvent was contacted with granular solid urea in an amount of about17.5% by wt. based on the filtrate and in the presence of 1.25% by vol.of water based on the .dewaxing solvent. The urea contacting operationwas carried out at ambient temperature of about 75 F. Substantiallyimmediately upon contact of the urea with the water-containing `filtrateurea complex formation occurred ,and the urea complex formation reactionwas substantially completely finished in less than about l0 minutes, thecontacting operation between the urea and the filtrate being carried outunder agitation or stirring.

Following the contacting operation the resulting solid urea-waxcomplexes were separated and decomposed in the presence of hot -tolueneat a temperature of about 170 F. Solid urea was thereupon recovered fromthis urea-Wax breaking operation and recycled to contact additionalfiltrate containing partially dewaxed oil and dewaxing solvent. Theresults of these tests are set forth in accompanying Table No. 1.

Urea dewaxing operations as applied tothe ltrate recovered from asolvent dewaxing operation and containing partially dewaxed oil anddewaxing solvent (SO/50 mixture of methyl ethyl ketone and toluene) werecarried out both in the presence and in the absence of water. It wasobserved that in a urea dewaxing operation carried out in accordancewith the practice of this invention wherein the dewaxing solventcontained a m It is seen therefore amount of water dissolvedtherein,such as an amount of water in the range G25-2.5% by vol., e.g. 0.9-1.25%by Vol., based on the dewaxing solvent, complexes of urea-wax weresubstantially immediately formed upon contact with urea and the urea-waxcomplex formation reaction was completed in about l0 minutes. On theother hand, when the urea dewaxing operations were carried out in thesubstantially complete absence of water even after 13 hours of contactwith urea the urea-wax` complex formation operation was not yetcomplete. In another test to show the iniluence of water upon theureawax complex formation reaction it was observed that when arelatively large amount of water was present within the urea complexformation reaction admixture, such as an amount of water of about 10% byvol. based on the reaction admixture or filtrate, the urea complexformation reaction was retarded. lt is desirable therefore thattheamount of water employed to enhance and improve the urea complexformation reaction be maintained at a relatively low level, such as anamount in the range 0.25-2.5% by vol. based on the dewaxing solvent orthe filtrate containing oil and dewaxing solvent.

As will be apparent to those skilled in the art many changes,modifications and alterations may be made in the practice of thisinvention without departing from the spirit or scope thereof.

We claim:

1. A method of ydewaxing a waxy petroleum oil fraction which comprisescontacting said waxy petroleum oil fraction with a dewaxing solventconsisting essentially of toluene and methyl ethyl ketone and a minoramount of water in the range 0.9-2.5% by vol. dissolved therein, theaforesaid contacting operation *being carried out at a relatively lowtemperature suicient to precipitate a substantial amount of wax fromsaid waxy petroleum fraction, sepa-rating the resulting precipitatedwax, recovering a liquid stre-am comprising dewaxed petroleum fractiondissolved in said dewaxing solvent yand containing said minor amount ofwater, contacting said liquid stream with urea under complex forming4conditions to form solid urea complexes with the straight chainhydrocarbons in the resulting dewaxed petroleum fraction and separatingthe resulting solid urea complexes.

2. A method of :dewaxing a waxy petroleum oil fraction which comprisescontacting said waxy petroleum oil fraction with a dewaxing solventconsisting essentially of toluene Iand methyl ethyl ketone and a minorlamount of water in the range (L9-2.5% by vol. dissolved therein, theaforesaid contacting operation being carried out at a relatively lowtemperature sufficient to precipitate a substantial amount of wax fromsaid waxy petroleum oil fraction, separating vthe resulting precipitatedwax, recovering a liquid stream comprising dewaxed petroleum oilfraction dissolved -in said dewaxing solvent and containing said rninoramount of water, cont-acting said liquid stream with urea under `complexformation conditions to form solid urea complexes with the straightchain hydrocarbons in the resulting dewaxed petroleum oil fraction,subjecting the resulting ladrnixture of urea, solid urea complexes,dewaxed petroleum oil fraction and dewaxing solvent to vacuumdistillation to remove the methyl ethyl ketone therefrom, separating byfiltration the solid urea `complexes and decomposing the separated solidurea complexes by contact wit-h toluene under complex breakingconditions to yield solid urea and recovering the resulting solid urea.

3. A method -as claimed in `claim 2 wherein the toluene used todecompose said separated urea complexes is separated by distillationfrom the resulting remaining admixture xafter separation of Isaidseparated urea complexes therefrom.

4. A method in accordance with claim 3 wherein `the urea formed duringthe decomposition of the urea cominorplexes is separated and recycled tocontact additional waxy petroleum fraction for the removal of w-axystraight chain hydrocarbons therefrom.

5. A method of dewaxing Ia waxy petroleum' oil tfraction which4comprises admixing said mixture with -a de- Waxing solvent consistingessentially of methylehhylketone and toluene `and containing 0.9 to 1.25vol. percent of Water therein to precipitate a substantial amount oflWax from said waxy petroleum oil fraction, separating the resultingprecipitate, contacting the resulting mother liquor containing saiddewaxing solvent containing said minor amount or" water therein withurea under conditions to effect the formation of sol-id urea complexeswith 10 l the Wax remaining :in said mother liquor `and separating theresulting solid urea complexes.

References Cited in the file of this patent UNITED STATES PATENTS2,577,202 Lien et al. Dec. 4, 1951 2,734,849 Gross etal Feb. 14, 19562,742,401 Knchen Apr. 17, 1956 2,786,015 Axe Mar. 19, 1957 2,823,172Rumlberger et `al Feb. `11, 1958 2,862,868 Brown et al Dec. 2, 19582,913,390 Brunstrum Nov. 17, 1959

1. A METHOD OF DEWAXING A WAXY PETROLEUM OIL FRACION WHICH COMPRISESCONTACTING SAID WAXY PETROLEUM OIL FRACTION WITH A DEWAXING SOLVENTCONSISTING ESSENTIALLY OF TOLUENE AND METHYL ETHYL KETONE AND A MINORAMOUNT OF WATER IN THE RANGE 0.9-2.5% BY VOL. DISSOLVED THEREIN, THEAFORESAID CONTACTING OPERATION BEING CARRIED OUT AT A RELATIVELY LOWTEMPERATURE SUFFICIENT TO PRECIPITATE A SUBSTANTIAL AMOUNT OF WAX FROMSAID WAXY PETROLEUM FRACTION, SEPARATING THE RESULTING PRECIPITATED WAX,RE-